1. Field of the Invention
The present invention relates generally to an improved process for forming fiber reinforced glass matrix or glass-ceramic matrix composite articles.
2. Description of the Prior Art
Because of the high density, temperature limitations, scarcity, and increasing expense of many conventional high temperature structural metals, increased attention has focused on non metal containing composites as replacements for conventional high temperature metal containing materials. Use of metal replacement high strength fiber reinforced resin and even high strength fiber reinforced metal matrix composites has progressed to the point of commercial acceptance in products ranging from sporting goods to automotive parts to advanced jet aircraft components. Such composite materials exhibit properties of high strength, toughness, and wear resistance. Additionally, frictional characteristics of composite materials, whether high or low, can be tailored to satisfy particular requirements.
Techniques have been disclosed which describe fabrication processes for making fiber reinforced glass and glass-ceramic composites, two of which are commonly assigned U.S. Pat. No(s). 4,324,843 and 4,613,473, the disclosures of which are incorporated herein by reference.
In the technique disclosed in U.S. Pat. No. 4,324,843, a tow of fibers, for example, silicon carbide, is continuously unwound from a spool at a moderate rate of speed and passed through a slip of powdered ceramic, liquid carrier and binder to impregnate the tow. The impregnated fibers are then rewound onto a larger rotating spool. An exemplary slip composition may be composed of 40 gm. of powdered glass ceramic and 780 ml. of water and 20 gm. of suitable organic binder such as that produced by Rhom and Haas Co. of Philadelphia, Penna. under the trademark "RHOPLEX". The coated fibers are then appropriately dried, forming a matrix impregnated tape. The matrix impregnated tape is then cut into desired lengths or shapes and laid up in proper fiber orientation, after which they are placed in an oven to burn off the binder. Then the lay-up is carefully placed in a mold and densified under heat and pressure forming the composite. Such densification is typically performed by hot pressing either under vacuum or inert gas such as argon in metal dies coated with colloidal boron nitride or graphite dies sprayed with boron nitride powder at pressures of 6.9-13.8 MPa (1000-2000 psi) and temperatures of 1100.degree.-1550.degree. C. Time of hot pressing will vary depending on composite makeup but generally will be accomplished between about 10 minutes and 1 hour.
In the technique disclosed in U.S. Pat. No. 4,613,473, glass, glass-ceramic or ceramic matrix material is formed into fibers. The technique then entails forming these fibers into yarn, then weaving, braiding, or knitting the yarn into a homogenous cloth of the matrix material. Thereupon, fibers of reinforcing material are prepared, then yarns of the reinforcing fibers, following which these yarns are then knitted or woven into a homogenous cloth of fiber reinforcement. In a subsequent step, a plurality of preforms of predetermined shape are cut from each of the cloths, the fiber reinforcing cloth preforms being interleaved with one or more layers of the matrix cloth preforms forming a lay-up. This lay-up is then placed in a die and densified under heat and pressure to form the composite article. The densification step is typically performed in the same manner as that indicated above with respect to the technique of the '843 patent.
There are a number of disadvantages associated with the densification step of these composite article manufacturing techniques, however. In a first instance, the equipment required is large, expensive, and costly to operate and maintain. Furthermore, it requires a substantial length of time in order to draw down the appropriate vacuum or provide the requisite inert atmosphere appropriate to the particular materials of the composite item.
Therefore, what is needed in this art is a method of manufacturing fiber reinforced composite articles which requires less costly equipment, has reduced energy requirements, and can achieve an end product in significantly less time.